Long term potentiation of synapses is believed to underlie learning and memory. This process starts with an influx of calcium which activates a large signaling network that causes the synaptic insertion of AMPA receptors, strengthening the synapse. Long term potentiation is a multi-step process including the transport of AMPA receptor-containing vesicles, exocytosis, and the diffusion of AMPA receptor into the synapse where they are actively maintained. Although each of these steps is critical, no one has specified the kinetics or location of these steps, which would be critical in understanding the process as a whole. While a variety of signaling molecules have been identified as modulators of long term potentiation, the connection between individual signaling molecules and specific outputs remains unclear. This proposal will use a reporter of surface AMPA receptors to investigate the kinetics of the exocytosis and synaptic retention stages of long term potentiation. Our two-photon imaging and uncaging system will allow us to image these processes on the single-spine level, and on the timescale of seconds. Furthermore, we will use pharmacological antagonists to identify which signaling molecules relay specific outputs of long term potentiation. Finally, we will image the activity dependent transport of an AMPA receptor scaffolding protein to determine its role in AMPA receptor trafficking. At the conclusion of this study, we will have elucidated the mechanisms of AMPA receptor trafficking during long term potentiation, and identified specific molecular pathways involved in the process. Identifying these pathways may aid drug development to alleviate excitotoxicity such as that induced by epilepsy. Also, the late stages of many diseases like Alzheimer's and Parkinson's Disease involve deficits of AMPA receptor function;further knowledge about the pathways mentioned above may provide new ways to alleviate the symptoms of these diseases.